API Extensions Handlers in the superscore

[doclzs]

There are two extensions handlers in the superscore:
API extensions handlers and user extensions handlers.

An API can add an API extension to the system 
initialization thread at three points:
immediately prior to driver initialization,
immediately after driver initialization,
and post thread context switch.

Why are these three points? Is there no need to
add API extensions to other points?

Thanks!

                         Bert
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